An information recording medium such as a video recording disc (e.g. DVDRAM) has spare areas. The spare areas are located at inner side and outer side of the innermost and outermost of a user data area of the disc, respectively.
For recording information on the disc, verification is performed after each writing procedure to check if there are defects in the user data area that records user data. A defect usually indicates a defective ECC block, which contains 16 sectors. If there are defects, replacements corresponding to the defects are stored into the spare area to be used as back-up blocks. Each of the spare areas is sequentially occupied and used from the outermost toward the innermost. In a case that six defects are found in the user data area, as shown in FIG. 1, corresponding replacements for the six defects are recorded in the spare area in a manner that the replacement for the first defect is recorded at the outermost location of the unused region of the spare area. The replacement for the second defect is inwardly recorded beside the first replacement, that is, the outermost location of the unused region, of which the area has been reduced due to the occupation by the first replacement. The rest can be deduced similarly.
The defect having the corresponding replacement thereof recorded is referred to a registered defect. The relationship information between the registered defects and the corresponding replacements, such as addresses, are recorded in a certain region of the disc, as commonly known in this field.
In a sequential reading procedure, a pick-up head of a reading apparatus reads the user data area 10 substantially from the innermost toward the outermost, as shown in FIG. 2. In FIG. 2 and other drawings, only the outer side spare area 20 is shown as an example for the sake of simplicity.
FIG. 3 illustrates the user data area 10 having defects 11, 13, and 15. As shown, the corresponding replacements 21, 23, and 25 are recorded in the spare area 20. In this example, the defect 11 is found in a fore writing/verifying process, so the corresponding replacement 21 thereof is recorded at the outermost among the three replacements. The defects 13 and 15 are found sequentially in one or respective writing/verifying processes later. Accordingly, the corresponding replacements 23 and 25 are arranged inwardly at the inner side of the replacement 21.
FIG. 4 schematically illustrates a conventional reading procedure. In this drawing, the bold arrows indicate reading operations of the pick-up head and the normal arrows indicate seeking operations of the pick-up head. The pick-up head sequentially reads data in the user data area 10. When the defect 13 is read, the pick-up head shifts to the spare area 20 to read the corresponding replacement 23, and then returns to the user data area 10 to read the data following the defect 13 until the next defect 15 is read. The pick-up head then jumps to the spare area 20 to read the corresponding replacement 25 to supplement the data for the defect 15. After reading the replacement 25, the pick-up head again returns to the user data area 10 to read the data following the defect 15 until the next defect 11 is read. The pick-up head once more jumps to the spare area 20 to read the replacement 21 corresponding to the defect 11 to supplement the data for the defect 11. Then the pick-up head returns to the user data area 10 to read the rest of the data. As described above, to obtain a complete data sequence in the sequential reading procedure, the pick-up head needs to shift back and forth between the user data area 10 and the spare area 20 for many times, as shown in FIG. 4.
Such frequent movements of the pick-up head for obtain corresponding replacements to replace the different defects of the user data area 10 may increase the load of the reading apparatus and degrades the stability thereof. Thus, the present invention brings a solution to the foregoing problem.